Process of making a highly dispersed mixture of carbon black and silicic acid

ABSTRACT

A highly dispersed homogeneous mixture of activated carbon black and activated silicic acid is formed by subjecting gaseous silicon monoxide or a mixture thereof with a gaseous metal oxide to the action of a gaseous oxidizing agent and passing substantially simultaneously a material that forms carbon black upon decomposition into the oxidizing zone or into the stream of gas right above the oxidizing zone.

United States Patent Illigen et al.

[451 May 2, 1972 [54] PROCESS OF MAKING A HIGHLY DISPERSED MIXTURE OFCARBON BLACK AND SILICIC ACID [72] lnventor's: Alfred llligen,l-Ieerbrugg, Switzerland;

Walter Neugebauer, Constance/Bodensee, Germany Deutsche Gold-undSilber-Scheideanstalt Vormals Roessler, Frankfurt, Germany [22] Filed:Sept. 24, I970 [21] Appl.No.: 75,130

[73] Assignee:

[56] References Cited UNITED STATES PATENTS 3,094,428 6/ l 963 Hamiltonet al. 106/307 2,578,605 l2/l951 Sears et al. l06/288 B PrimaryExaminer-James E. Poet Atmrney-Michael S. Striker [5 7] ABSTRACT Ahighly dispersed homogeneous mixture of activated carbon black andactivated silicic acid is formed by subjecting gaseous silicon monoxideor a mixture thereof with a gaseous metal oxide. to the action of agaseous oxidizing agent and passing substantially simultaneously amaterial that forms carbon black upon decomposition into the oxidizingzone or into the stream of gas right above the oxidizing zone.

1 1 Claims, 4 Drawing Figures 'PATENTEDMAYZ I972 8,660,132

SHEET 10F 2' I FIG. I

OOOOOOOO Z 202 24 o o o o o o 0 o FIG. 2

INVENTCP a: IZIII'W a. new sane-4 Adm- I, 11..

ATTORNEY.

PROCESS OF MAKING A HIGHLY DISPERSED MIXTURE OF CARBON BLACK AND SILICICACID BACKGROUND OF THE INVENTION The invention relates to a process ofmaking highly dispersed mixtures consisting predominantly of activatedcarbon black and activated silicic acid.

Highly dispersed materials, that is both inorganic white fllers orpigments, for instance titanium dioxide, aluminum oxide and silicondioxide as well as black fillers (carbon black), are widely applied inmany areas of chemical technology, particularly as reinforcing fillersin rubber compositions and synthetic elastomers. By far the mostimportant highly dispersed fillers are silicon dioxide (activatedsilicic acid) and carbon black (activated carbon black). The reinforcingproperties of these materials usually appear only when they are presentin a very fine distribution. This normally implies a material whichpossesses a specific BET surface above about 50 mlg.

' In conventional processes, silicic acid is principally obtained by wetprecipitation from alkali silicate solution by means of acids. Morerecently, processes have become known for 'making highly dispersedsilicic acid which involve the flame hydrolysis of silicon tetrachlorideand the oxidation of gaseous silicon monoxide. Carbon black inindustrial practice is usually obtained by the thermal decomposition orincomplete combustion of carbon compounds.

The usefulness of activated carbon black is mainly based on itshydrophobic organophilic properties, while that of the activated silicicacid is due to its hydrophilic properties. There are, however,applications where it is desirable to make use both of the properties ofactivated carbon black and of activated silicic acid. Attempts havetherefore been made to employ both materials at the same time. However,this required that both materials be present in a perfect mixture, sinceonly then is it possible to obtain the desired action inv a uniformmanner in the entire range of mixtures. v

However, mixtures of silicon dioxide and carbon black formed bymechanical mixing operations either prior to incorporation in the finalproduct or thereafter have so far been obtained in a homogeneous mixtureonly to a very limited extent. Usually there is obtained a mixture onlyof agglomerates of silicon dioxide and carbon black.

Efforts have therefore been made in numerous cases to obtain improvedproducts. For instance, according to a priorpart procedure (US. Pat. No.2,156,591) carbon-containing silicic acid is made by pyrolysis from amixture of tar and kieselguhr in the absence of air.

' It has also been proposed (US. Pat. No. 3,094,428) to make metaloxide-carbon black mixtures by decomposing metal compounds andunsaturated hydrocarbon compounds, particularly, acetylene or benzene inan oxygen-containing reducing flame to obtain metal oxide-carbon blackmixtures wherein carbon black is present up to 50 percent. Anotherprior-art procedure (US. Pat. No. 2,632,713) proposes to introducecombustible compounds of silicon, boron or germanium into the flame of aspecial carbon black burner. As combustible compounds there areparticularly proposed orthoesters, hydrogen-containing or metal-organiccompositions. The mixtures obtained contained a maximum of percent ofthe oxides of silicon, boron or germanium.

All these processes involve a number of shortcomings. The mixturesobtained are inactive because they have too large a particle size. Themixing ratio of carbon black and metal oxides is rather limited. Themetal compounds introduced into the mixture are attached to elementssuch as chlorine which have a corrosive effect. The compounds also maybe too expensive or dangerous to handle. The flue gases originating inthese processes have nor or only a very limited calorific value.

It is therefore desirable to provide for a process of making silicondioxide-carbon black mixtures in which the silicon dioxide primaryparticles, as well as the carbon black primary particles, may be causedto originate simultaneously and to form an intimate mixture immediatelyupon their formation. This process then would not incur the previouslylisted shortcomings.

The present invention also has the object to provide for a process ofmaking highly dispersed homogeneous mixtures consisting predominantly ofactivated carbon and activated silicic acid which process is effectiveby reaction of metal oxides and silicon oxides or silicon oxides alonewith carbon compounds which will lead to products that can be used asreinforcing fillers for rubber elastomers.

SUMMARY or THE INVENTION These and other objectives are attained by theprocess of the invention wherein gaseous silicon monoxide or a mixturethereof with a gaseous metal oxide is subjected to the action of agaseous oxidizing agent in an oxidizing zone and wherein a material thatforms carbon black upon decomposition is passed either directly into theoxidizing zone or immediately thereafter into the flow of gas emanatingtherefrom. There is thus formed substantially simultaneously thedecomposition of the carbon black-forming material and the formation ofthe mixture of activated silicic acid and activated carbon black.

I The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to details of construction andprocedure, will be best understood from the following description ofspecific embodiments when read in connection with the accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION OF THE INVENTIONAND OF PREFERRED EMBODIMENTS The important feature of the invention isthe formation of homogeneous mixtures within the primary particle rangewhich is obtained by pyrolytic reactionof silicon oxides or mixtures ofsilicon oxides and metal oxides with carbon compounds in the gaseousphase. This is accomplished by reacting 1 the gaseous silicon monoxide,or the mixture thereof with gaseous metal oxide, with a gaseousoxidizing agent inan oxidation zone and passing the carbon blackfurnishing materials directly into the oxidation zone or immediatelysubsequent thereto into the flow of gas emanating from the oxidationzone in order to effect the decomposition of the carbon black formingmaterials. Surprisingly, it is possible in this manner to obtain highlydispersed homogeneous silicon dioxide and carbon black-containingmixtures and, if desired, mixtures which in addition contain siliconmonoxide and silicon carbide. The mixture in these cases is formedduring the formation of the components and therefore in the area of theprimary particles. Thus, the optimum combination of properties of theindividual components is possible.

Gaseous silicon monoxide is a chemically highly reactive material which,as is well known, can easily be reacted with oxidizing agents such asair or steam to form silicon dioxide and can be reacted with reducingagents such as hydrocarbon compounds to form silicon carbides.

It was unexpected and is surprising that the oxidation of the siliconmonoxide to silicon dioxide and the decomposition of thecarbon-containing compounds to form carbon black can be effectedvirtually simultaneously without any material interference with theindividual reactions. It appears that the gaseous silicon monoxidecombines preferentially, that is with greater speed, with the availableoxygen than with the availaygen apparently combines preferentially withsilicon monoxide to form silicon dioxide rather than with carboncompounds to formcarbon monoxide.

' The drawings explain the reaction and suitable apparatus therefor in aschematic manner. With reference particularly to FIG. 1, it will benoted that a stoichiometric mixture of quartz (Si0,) and coke, or aquartz and silicon mixture is continuously introduced through an inlet101 into an electrothermal furnace 1 wherein, for instance, an electricarc is formed. The gaseous silicon monoxide formed at the highertemperature within the furnace then flows through an outlet 2, the gasmixture possibly containing carbon monoxide. Directly above the outlet 2a gas mixing chamber 3 is provided which has two super-imposed chambers2' and 3 with inwardly directed bores which permit to mix the siliconmonoxide containing gas current with additional gases or liquids- Theagent necessary to oxidize the silicon monoxide and, if present, thecarbon monoxide such as air may for instance be introduced through theduct 102. Through duct 103 the compound which decomposes into carbonblack is introduced. The decomposition, therefore, takes placeimmediately within the oxidation zoneor directly above it in chamber 4which.

preferably is provided with a heat insulation.

The reaction product thus formed is suspended in the gas current whichis passed through duct 105 to a heat exchanger 5 and subsequently to aseparator 6 from which the solid product is passed through a valve 7into a receptacle 8. The residual gas is moved by suctionfrom aventilator 9 through the duct 106 and then through duct 107 for removalfrom the operation. If the gas is to be circulated, however, it can bepassed through duct 104 back into the mixing chamber 3. Excess gas canbe removed through, duct 107, if desired, by means of valves 10 and 11.

FIGS. 2-4 show various embodiments of the mixing device 3. The siliconmonoxide-containing current of gas enters the lower partof this devicefrom below. With reference particularly to FIG. 2, it will be seen thatthe chamber 21 is provided to receive a cooling agent, for instancewater or oil. The agent, which is required for oxidizing the siliconmonoxide, such as for instance air, oxygen or water, enters thesuperimposed chamber 22 through an inlet 202 and leaves the chamber bymeans of bores 24 which are arranged in an annular manner. The directionof the bores can be such that the oxidizing agent enters the-hot siliconmonoxide gas flow at right angles or at a desirable angle ofinclination.

The size and number of the bores should be commensurate with the amountof oxidizing agent fed into the device and the available cross-sectionof the mixing chamber in order to perinit the oxidizing agent topenetrate into the center of the silicon monoxide gas current.

The decomposable carbon compound is introduced into the chamber 23through an inlet 203 and leaves the chamber through bores 25.

The bores 25 in the embodiment of FIG. 2 are arranged to permit thedecomposition of the carbon black forming compound directly above thesilicon monoxide oxidation zone.

" This results in a higher decomposition speed. The bores 35 in FIG. 3,on the other hand, are arranged in the top face of the chamber 31. Thispermits to obtain a larger reaction space for the decomposition, but therelative share of combustion or the decomposable material will besmaller in this case.

FIG. 4 illustrates an embodiment where the oxidation agent enters fromchamber 42 through a circle of inlet openings 46 while the decomposablecarbon compound enters through annularly arranged apertures 45 fromchamber 43.

The decomposition of the carbon black-forming compound is effected bythe high heat of reaction which occurs with the oxidation of the gaseoussilicon monoxide and possibly carbon monoxide by oxygen which latter maybe present also in the form of air, steam or carbon dioxide. Heatadditionally is furnished by the heat contents of the silicon monoxidewhich leaves the mixing chamber at a temperature of 2000 C and whichalso may contain carbon monoxide. Since the decomposition reaction takesplace'directly in the gaseous phase, it

has a high thermal efficiency and forms the most effective use of theheat liberated with the formation of silicon dioxide from the siliconmonoxide.

In the conventional devices and processes where chilling was effected byblowing in of an excess of air at the place of the SiO, formation inorder to get a finely divided product the oxidation heat was reduced toa temperature level which was of little practical interest and forpractical purposes was thus completely destroyed. The present invention,on the other hand, permits to incorporate the carbon black in thesilicic acid practically at the price of the crude material.

The amount of the oxidizing agent should be sufficient on the one handto permit as much oxidation of the silicon monoxide to silicon dioxideas possible and on the other hand to keep at a low level the combustionof the decomposable material which is introduced into the reaction.Preferred is an amount of oxidizing agent which is slightly below orabove the stoichiometric amount. However, useful results were stillobtained with a three-times to five-times excess.

The mixing ratio of SiO to carbon black can be adapted in a wide range,to the ultimate use of the product. It depends also on the type andamount of the introduced decomposable compound. The mixtures formed inthe process of the invention are compositions of a grey to deep blackcolor depending on the amount of decomposable carbon black furnishingcompound and, accordingly, have a specific surface of between 50 and 200m lg. They have a homogeneous appearance and in the electron microscopeat an enlargement of 50,000zl have particle sizes between 5 and 300millimicrons. The electron microscope enlargements show that silicicacid and carbon black are present in the primary particle area inhomogeneous statistically uniform distribution.

The decomposable materials preferably are hydrocarbons such as lower tointermediate aliphatics and olefins, acetylene, aromatic compounds,anthracene oils, distillation residues and mixtures of these variousmaterials. Depending on the type of material and the conditions of thereaction, the decomposition leads to varying yields of carbon black. Thedecomposition may lead to smaller or larger amounts of olefines in theproduct produced. In such cases, it may be-helpful to recirculate theflue gas from which the solids have been separated into the process orto remove the olefinsfrom the flue gas and reintroduce them into theoperation.

The gaseous products which are formed in decomposing the carboncompound, such as hydrogen, methane, and olefins cause the gas currentto have a high calorific value based also on the carbon monoxide fromthe electric arc furnace. The easiest way tomake use of this calorificvalue is by using it for heating. For instance, with use of ligroin ascarbon blackforming compound and air as oxidizing agent for the siliconmonoxide a flue gas was obtained containing 18 volume-percent hydrogen,15 volume-percent carbon monoxide, 7 volume-percent methane and 4volume-percent ethane.

The reaction products, in addition to silicon dioxide and carbon black,may also contain portions of nonreacted silicon monoxide which eithermay show up as solid SiO or in the form of the disproportionationproducts Si and SiO and the reaction product may also contain siliconcarbide. These products are present like the main products, silicondioxide and carbon black, in a highly dispersed form and in superfinedistribution. Undesirable effects of these additives have not beennoticed.

It is a particular feature of the process of the invention thatadditional materials which are of importance for the use as rubberadditives may be added to the SiO /carbon black mixture in finelydistributed form. Among these are materials which under the conditionsof the SiO gas generation may be converted to the gas phase and then maybe precipitated in highly dispersed form during the oxidation andsubsequent cooling. Among such materials, in addition to, for instance,aluminum oxide and magnesium oxide, is zinc oxide which is an importantcomponent of many elastomer mixtures. This can be accomplished simply byadding a corresponding amount of zinc oxide to the quartz-coke initialmixture.

as nitrogen, hydrogen or a noble gas. The introduction of 5 these gasespreferably is effected through bores in the graphite electrode orthrough tubes of silicon carbide which pass through the topplate of theelectric arc furnace.

The following examples will further illustrate the invention.

EXAMPLE 1 A mixture of quartz sand and coke fines at a ratio of 5:1 wasreacted in an electric arc furnace. There was thus obtained an hourlyoutput of 3.8 kg of gaseous silicon monoxide and 2.4 kg carbon monoxide.The gas current left the furnace at a temperature between 2,000 and2,500 C. It then passed through the gas-mixing device as shown in FIG. 3of the drawings. Twelve Nm of air were added in chamber 22 and 7.4 Nmpropylene were added in chamber 23. A deep black product was separatedin the separator. The product had a specific surface of 69 m lg and apour weight of 27 g/l. The chemical analysis showed a content of 55weight-percent SiO 31 weightpercent carbon black and 11 weight-percentsilicon carbide. The benzene-soluble fraction was 2 weight-percent.

Electron microscope enlargements at a scale of 50,000:l showed roundprimary particles of SiO of a size between about 5 and 300 millimicronsand irregularly formed, for instance flake-shaped, carbon black primaryparticles of a size between about 5 and 100 millimicrons, both types ofparticles being uniformly distributed throughout.

EXAMPLE 2 In a similar apparatus and in the same manner as in Example 1,7.6 Nm air/h and 7.0 Nm" ethylene/h were introduced into the hot SiO-COgas current. The product obtained had a specific surface of 52 m lg, apour weight of 27 g/ l and a composition of 52 weight-percent SiO 25weight-percent carbon black and 18 weight-percent SiC. Thebenzene-soluble fraction was 8.3 weight-percent.

' EXAMPLE 3 The process was the same as in Example 2, but an hourlyamount of air was used of 26 Nm and ethylene of 6 Nm. The obtained blackproduct had a'specific surface of 174 m lg, an SiO content of 71weight-percent and a carbon black content of 24 weight-percent.

EXAMPLE 4 Oxygen and anthracene oil were fed into a gas current ofsilicon monoxide and carbon monoxide at a temperature between about2,000 and 2,500 C. A gas-mixing chamber was used as shown in FIG. 3. Adeep black product was obtained with a specific surface of 1 14 m /g anda composition of 48 weight-percent SiC- 48 weight-percent carbon black,2 weight-percent SiC, and l weight-percent Si.

EXAMPLE 5 Eight and one-half kg of a mixture of quartz chips andfractionated silicon at a ratio of 2.1:1 was continuously introducedinto an electric arc furnace. The gas mixing chamber employed was thatshown in FIG. 2. Through the chamber 22 there were introduced at anhourly rate 14 Nm of air into the silicon monoxide gas current emanatingfrom the electric arc furnace. Through chamber 23 14 l petrol ether(liquid) were introduced hourly through correspondingly small bores. Theproduct obtained had a specific surface of 74 m /g., a pour weight of 29g/l and contained 74 weight-percent of SiO and weight-percent of carbonblack. The electron microscope showed'a homogeneous distribution of Si0and carbon black in the area of primary particles.

EXAMPLE 6 A gas stream containing about 3.7 kg gaseous silicon monoxideand 2.4 kg carbon monoxide was produced each hour in an electric arcfurnace. Through a mixing chamber as shown in FIG. 2 there wereintroduced 5 Nm air/h through chamber 22 and 7 l ligroin (boiling point-l00 C) through chamber 23. The ligroin was in vapor form. The obtainedblack product had a specific surface of 93 mlg and a pour weight of 29g/l. The chemical composition was 54 weightpercent SiO 21 weight-percentcarbon black, 4 weight-percent Si and 1 weight-percent SiC. The flue gashad the following composition: 18 volume-percent H 15 volume-percent C0,7 volume-percent CH 4 volume-percent C 11 31 volume-percent CO 40volume-percent N the balance formed by other carbon-containing gas.

EXAMPLE 7 A gas current of 3.8 kg silicon monoxide and 2.4 kg carbonmonoxide was produced in an electric arc furnace. The gas was passedinto a mixing chamber as shown in FIG. 2. From the lower chamber 22 5 Nmair/h were introduced through 60 apertures which had an inclinationagainst the SiO-CO gas current at an angle of 45. In chamber 23 8.5 Nmethylene/h were introduced through 60 bores at an angle of inclinationto the SiC-containing gas current of 60. There was obtained a dark graymixture comprising 23 weight-percent SiO 20 weight-percent carbon black,17 weight-percent SiO and 41 weight-percent SiC with a specific surfaceof 92 m /g.

EXAMPLE 8 The gas current in this case contained 3.8 kg silicon monoxideand 2.4 kg carbon monoxide per hour and had a temperature between 2,000and 2,500 C. The mixing chamber employed was that of FIG. 4. From thechamber 42 oxygen was introduced at an hourly rate of 1.6 Nm and fromchamber 43 an hourly rate was introduced of 3.0 Nm of a commerciallyavailable C /C LPG. There was obtained a dark gray highly dispersedmixture comprising 62 weight-percent SiO l3 weight-percent carbon black,13 weight-percent SiO and 13 weight-percent SiC which had a specificsurface of m /g and a pour weight of 37 g/l.

EXAMPLE 9 The same process was used as described in Example 5. However,additionally, 6 Nrn argon were introduced each hour into the electricarc furnace through bores in the electrodes. The final product in theform of a highly dispersed mixture had a specific surface of 93 m /g, apour weight of 28 g/l, and a chemical composition of 67 weight-percentSiO 28 weight-percent carbon black, 2 weight-percent Si and 3weight-percent SiC.

EXAMPLE l0 Employing the same method as in Example 9 there were usedinstead of the argon an amount of 5 Nm hydrogen. The mixture obtainedhad a specific surface of 89 m lg, a pour weight of 28 g/l and achemical composition of 66 weight-percent SiO 28 weight-percent carbonblack, 4 weight-percent Si and 2 weight-percent SiC.

EXAMPLE 11 In this case a current of gas was produced containing eachhour 3.8 kg silicon monoxide and 2.4 kg carbon monoxide. The gas mixingdevice was that shown in FIG. 2. From the chamber 22 5 Nrn steam andfrom chamber 23 5 Nm propylene were introduced. There was obtained aproduct containing 69 weight-percent SiO and 22 weight-percent carbonblack. It had a specific surface of 61 m /g and a pour weight of 35 g/l.The product was distinguished by particularly high hydrophobicproperties.

EXAMPLE 12 In an electric arc furnace a mixture was converted to a gasphase comprising per hour 5.5 kg quartz sand, 1.1 kg petrol coke, and0.45 kg zinc oxide. The gas chamber was the one shown in FIG. 3. Throughchamber 22 8 Nm air/hr and through chamber 23 14 liters petrol ether perhour were introduced into the hot gas current. At the separator a blackproduct was removed containing 64 weight-percent SiO 26 weight-percentcarbon black and 5.3 weight-percent ZnO. The specific'surface of theproduct was 73 m /g.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications withoutomitting features that,from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended l. The process of making a highly dispersedhomogeneous mixture consisting-predominantly of activated carbon blackand activated silicic acid, the said process comprisingsubjectinggaseous silicon monoxide to the action of a gaseous oxidizing agent inan oxidizing zone at a temperature of at least 1 about 2000 C to oxidizethe silicon monoxide to silicon dioxide and passing a material thatforms carbon black by decomposition at the reaction temperature in theformed gaseous silicon dioxide current while the same is at saidtemperature thereby causing the decomposition of said carbon blackforming material and,.substantially simultaneously therewith, causingthe fonnation of said homogeneous mixture of activated carbon black andactivated silicic acid.

2. The process of claim 1, wherein the carbon black forming material ispassed into the silicon dioxide gas current immediately after it hasleft said oxidizing zone.

3. The process of claim 1, wherein the oxidation of the silicon monoxideis effected in the presence of carbon monoxide. t

4. The process of claim 1, wherein the oxidation is effected by passingoxygen, air or water into said gaseous silicon monoxide at a temperatureof about 2,000 to 2,500 C.

5. The process of claim 1, wherein the gaseous silicon monoxide isformed by reacting quartz with a member selected from the groupconsisting of silicon and coke in an electric arc furnace. v

6. The process of claim 1, wherein the gaseous silicon monoxide isdiluted with a gas selected from the group consisting of hydrogen,nitrogen and a noble gas prior to passing into said oxidation zone.

7. The process of claim 1, wherein the gaseous silicon monoxideadditionally contains a metal oxide that is volatilizable under theconditions of the oxidation reaction.

8. The process of claim 7, wherein the metal oxide is a member selectedfrom the group consisting of aluminum oxide, magnesium oxide, zinc oxideand a mixture of at least two of these oxides.

9. The process of claim 1 wherein the carbon black forming material is ahydrocarbon compound.

10. The process of claim 9 wherein the hydrocarbon compound is a memberselected from the group consisting of lower or intermediate aliphatic orolefinic hydrocarbon compounds, acetylene, aromatic compounds and amixture of such compounds.

11. The process of claim 10, wherein the aromatic compound is ananthracene oil.

it III

2. The process of claim 1, wherein the carbon black forming material ispassed into the silicon dioxide gas current immediately after it hasleft said oxidizing zone.
 3. The process of claim 1, wherein theoxidation of the silicon monoxide is effected in the presence of carBonmonoxide.
 4. The process of claim 1, wherein the oxidation is effectedby passing oxygen, air or water into said gaseous silicon monoxide at atemperature of about 2,000* to 2,500* C.
 5. The process of claim 1,wherein the gaseous silicon monoxide is formed by reacting quartz with amember selected from the group consisting of silicon and coke in anelectric arc furnace.
 6. The process of claim 1, wherein the gaseoussilicon monoxide is diluted with a gas selected from the groupconsisting of hydrogen, nitrogen and a noble gas prior to passing intosaid oxidation zone.
 7. The process of claim 1, wherein the gaseoussilicon monoxide additionally contains a metal oxide that isvolatilizable under the conditions of the oxidation reaction.
 8. Theprocess of claim 7, wherein the metal oxide is a member selected fromthe group consisting of aluminum oxide, magnesium oxide, zinc oxide anda mixture of at least two of these oxides.
 9. The process of claim 1,wherein the carbon black forming material is a hydrocarbon compound. 10.The process of claim 9 wherein the hydrocarbon compound is a memberselected from the group consisting of lower or intermediate aliphatic orolefinic hydrocarbon compounds, acetylene, aromatic compounds and amixture of such compounds.
 11. The process of claim 10, wherein thearomatic compound is an anthracene oil.